This subproject is one of many research subprojects utilizing the resources provided by a Center grant funded by NIH/NCRR. The subproject and investigator (PI) may have received primary funding from another NIH source, and thus could be represented in other CRISP entries. The institution listed is for the Center, which is not necessarily the institution for the investigator. Changes in dermal capillary blood flow and blood oxygen deliver to deep tissue in response to a breif period of hypoxia will be studied in normal controls and subjects with sickle cell anemia. These responses will be standardized so they can later be used to study pharmacological interventions that may improve blood flow and oxygen delivery. Blood oxygen level delivery will be measured by magnetic resonance imaging and dermal capillary blood flow will be measured using laser-Doppler flow.